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Glossary of Thermography Terms

For your information we have compiled a Glossary of Thermographic Terms in alphabetical order.

Absolute Zero

The temperature that is zero on the Kelvin temperature scale. The temperature at which no molecular motion takes place in a material. -273.15°C.

Does not occur naturally, not even in outer space.

Absorbtivity, α (Absorptance)

The proportion (as a fraction of 1) of the radiant energy impinging on a material’s surface that is absorbed into the material. For a blackbody, this is unity (1.0). Technically, Absorbtivity is the internal absorptance per unit path length. In thermography, the two terms are often used interchangeably.

Accuracy (of Measurement)

The maximum deviation, expressed in % of scale or reading (depending on measurement range and instrument dynamics) or in degrees Celsius, that the reading of an instrument will deviate from a correct standard reference.

Ambient Operating Range

Range of ambient temperatures over which an instrument is designed to operate within published performance specifications.

Ambient Temperature

See Reflected Apparent Temperature (RAT)


Any irregularity, such as a thermal anomaly on an otherwise isothermal surface. Any indication that deviates from what is expected.

Apparent Temperature

The target surface temperature indicated by an infrared point sensor, line scanner or imager without compensation for measurement (Object) parameters.


A product of artificial character due to extraneous agency; an error caused by an uncompensated anomaly. In thermography, an emissivity artefact simulates a change in surface temperature but is not a real change. A hot solar reflection or a cold reflection due to narcissus would be examples of artefacts.

Atmospheric Temperature

The temperature of the atmosphere between the camera and the object.

Atmospheric Windows (Infrared)

The spectral intervals within the infrared spectrum in which the atmosphere transmits radiant energy well (atmospheric absorption is a minimum). These are roughly defined as 2-5 µm and 8-14 µm.

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